Project Summary The objective of the research is to develop patient iPSC-based HTS assays that can facilitate therapeutic discovery for treating biliary atresia (BA) fibrosis. BA is the most common cause of pediatric end-stage liver disease in the U.S. and is inevitably fatal within the first two years of life if untreated. Notably, BA is the most rapidly fibrosing liver disease in humans and is associated with significant morbidity and mortality in children. Compared to other liver diseases that gradually progress into cirrhosis over decades, BA infants characteristically develop fibrosis/cirrhosis within weeks to months after birth. Although there is a palliative surgical procedure, there is no known treatment to halt the progressive fibrosis; most infants born with the disease will need liver transplantation in order to survive. A main challenge in developing effective anti-fibrotic drugs has been the lack of a model of the human disease. The human induced pluripotent stem cell (iPSC) technology provides an alternative for generating functional, renewable and relevant cell sources for disease modeling using patient tissues. Based on our expertise on in vitro disease modeling, we have recently succeeded in developing BA patient- specific iPSCs and have demonstrated that these cells produce significantly more collagen and other fibrosis markers along with deficiency in biliary differentiation (key disease features of BA), compared to the iPSCs of healthy children. This new line of research on BA patient iPSCs makes it feasible to evaluate both efficacy and safety of potential drugs in a more human-relevant setting. Thus we believe this human cellular model of BA can serve as an ideal system to identify effective anti-fibrotic compounds in treating liver fibrosis in BA. In the current study, we propose to: 1) Develop a novel high throughput assay to assess anti-fibrotic effects of compounds on BA fibrosis using COL1A1 reporter BA-iPSC lines. We will determine the conditions for miniaturizing the assay and for robust assay automation. 2) Perform pilot screens to validate and optimize the assay using a clinical drug library in order to ensure automation reliability and assay reproducibility. 3) Develop independent secondary assays to prioritize hit selection by further verifying the anti-fibrotic effects of the hits and evaluating their protective/adverse effects on hepatobiliary tissues derived from patient iPSCs. At the conclusion of this study, we will have developed a robust, patient cell-based HTS assay capable of identifying new disease targets and leads for developing novel therapies for BA patients. Moreover, success of this project will be a step forward in translating basic iPSC discoveries to therapeutic applications, helping to fulfill their promise in developing regenerative medicine.